Screen grid relay circuits



Sept. 25, 1934. w BUSCHBECK 1,974,912

SCREEN GRID RELAY CIRCUITS Filed Jan. 25, 1933 INVENTOR IVER/ EliBUSCHBtZ/l ATTORNEY I sary to choose the neutralizing capacity =1 monicthereof.

= nating current potentials- Patented Sept. 25, 1934 -UNITED STATESSCREEN can) RELAY cmcurrs Werner Busclibeck, Berlin,

Telefunken Gesellschaft fiir Germany, assignor to Drahtlose Telegraphicm.'b. 11., Berlin, Germany, a corporation of Germany Application January 25,

1933, Serial No; 653,419

In Germany February 29, 1932' 4 Claims.

This invention relates toneutralizing circuits for screen grid tubes. Inorder to secure a sufficient freedom from reaction in screen'grid tubes,it is necessary that the'screen grid actually carries cathodepotential.- This requirement can no longer be easily complied with inparticular in the case of short wavesand high anode potentials, sincethe current Js, passing across the anode screen grid capacity, causes avoltage drop in the lead, which always requires a certain length,connecting the screen grid with the cathode, or in the screen gri-dblock condenser respectively. This voltage drop may only be kept smallby decreasing the current flowing through this lead which, in accordancewith the present invention, may be obtained by a bridge circuit in whichthe screen grid connection and the cathode point K become points ofequal potentials. To this end it is simply necesof the screen grid insuch a manner so as to fulfill the equation The nature of the inventionand the manner in which the invention may be carried out will bedescribed more in detail hereinafter.

In describing the invention reference will be made to the drawing,throughout which like reference characters indicate like parts, and inwhich:

Figure 1 serves to illustrate the novel features of this invention;while,

Figures 2, 3 and 4 show relay circuits including screen grid repeatersarranged in accordance with the present invention.

Referring to Figure 1, 2 indicates an inductance connected between thecontrol grid 4 and cathode 6 of a screen grid tube 8. The inductance 2may be coupled to any source of ultra high fre- E. quency oscillationsto be relayed and/ or amplified.

10 indicates a tuned circuit coupled between the anode 12 and cathode 6of tube 8 by way of a potential source 14. The circuit 10 may be tunedto the fundamental frequency or to a har- The screen grid electrode 16may be charged by way of an inductance 18 from the source 14. In shortwave work it is desirable that the screen grid electrode 16 bemaintained at ground potential with respect to the alter- This isaccomplished by connecting the screening grid electrode direct- 1y tothe cathode by way of a by pass condenser Bs, as shown. The connectingleads, even under thebest of conditions, must have some length andtherefore there is a voltage drop caused by the current Js flowing inthe connecting leads; Also, the capacity Bs, offers some impedance tothe alternating currents J s causing a further potential drop betweenthe screen grid electrode and the cathode. This potential drop may onlybe kept small by reducing or decreasing the current flow in the screengrid lead including the capacity Bs. A reduction in the flow of currentin this lead may be accomplished by the utilization of a bridge circuit,as disclosed in Figure 2.

In Figure 2 the screen grid electrode 16 is connected directly to apoint S at one corner of a bridge circuit, the other corner K of whichis connected to the cathode. The capacity between the anode 12 andscreen grid electrode 16, indicated by the dotted condenser CSAconnected between the points A and S, forms one arm of the bridge,another arm of which is formed by a capacity C1 which may include thecapacity between the anode and cathode 6, and a third arm of whichincludes a capacity C2. The screen grid neutralizing capacity CNS is nowchosen in such a manner to fulfill the equation In this circuit thepoints S and K are at the same potential with respect to alternatingcurrents, but the point K is at cathode potential. Therefore, there isno current flowing between the screen grid 16 and cathode 6.

In Figure 3 the screen grid electrode 16 is also connected in a balancedbridge circuit in such a manner that there is no potential drop withrespect to the alternating currents relayed in the tube 8 between thescreen grid and the oathode. Here the anode to control grid electrodecapacity is shown by dotted lines at CAG.

This bridge circuit does not render the arrangement more complicated asmay at first be expected, since for short waves the remaining amount ofgrid-anode capacity must in the most cases be neutralized despite thepresence of the screen grid for which purpose a bridge circuit isrequired at any case (Figure 3).

Moreover, in the case of the pushpull arrangements of screen grid tubes,the screen grid capacity of the pushpull tube can be used at the loo ins

same time as neutralizing capacity for the screen grid (Figure 4).

Having thus described my invention and the operation thereof, what Iclaim is:

1. In combination with a screen grid amplifier, a source of ultra highfrequency currents coupled between the control grid and cathode, anoutput circuit connected to the anode of the amplifier, a source ofpositive screen grid potential connected between the screen grid andcathode, a radio frequency condenser connected between the screen gridand cathode in shunt with said potential source, and a capacity bridgeconnected in said output circuit, said screen grid and cathode beingconnected to conjugate points/on the bridge.

2. In combination with a screen gridamplifier, a source of ultra highfrequency currents coupled between the control grid and cathode, anoutput circuit connected to the anode of the amplifier, a source ofpositive screen grid potential connected between the screen grid andcathode, a radiofrequenc'y condenser connected between the screen gridand cathode in shunt with said potential source, and a capacity bridgeconnected in said output circuit, said screen grid and cathode. beingconnected to conjugate points on the bridge, and one arm of said bridgecomprising the screen grid-anode capacity of said amplifier. 3. Incombination with a screen grid amplifier,

a source of ultra high frequency currents coupled between the controlgrid and cathode, an output circuit connected to the anode of theamplifier, a source of positive screen grid potential connected betweenthe screen grid and cathode, a radio frequency condenser connectedbetween the screen grid and cathode in shunt with said potential source,and a capacity bridge connected in said output circuit, said screen gridand cathode being connected to conjugate points on the bridge, and saidshunt condenser being connected connected between said ultra highfrequency current source and said output circuit in push pull relationto said first screen grid amplifier, said bridge being connected betweenthe screen grid and cathode of said second amplifier tube.

WERNER BUSCI-IBECK.

